Abstract:

The present invention pertains to a method for incessantly producing
polysilicon ingots, especially fabricated of an equality polycrystalline
material. It contains a metallurgical method for continuously producing
large amount of polysilicon ingot made by metal silicon, further
comprising the steps of aligning empty graphite molds on furnace cars;
preheating the molds in the preheating area; pouring the liquidized
silicon into the preheated molds; transporting the molds filled with
liquidized silicon from the high-temperature area, thence to a
medium-temperature area, and then to a low-temperature area for
solidifying the liquidized silicon into crystallized silicon; cooling the
crystallized silicon until reaching the room temperature by the
assistance of a shroud in a rotary conveyer track, thus generating an
integral polysilicon ingot. The apparatus comprises a body, a chamber, a
track, cars, a front and rear auxiliary cars, a rotary conveyer track, a
propulsion apparatus, and an adjusting system.

Claims:

1. A directional solidification method for incessantly producing
polysilicon ingot comprising the steps of:axially and sequentially
arranging a plurality of empty graphite molds in alignment on furnace
cars; said molds being driven by removals of said cars along with a
furnace track within a furnace chamber and preheated in a temperature
range from 1200 degree C. to 1600 degree C. while traveling in a
preheating area of said furnace chamber;pouring a certain amount of
liquidized silicon from a furnace hopper into said preheated molds;
wherein, said furnace hopper being disposed on a crown of a
high-temperature area, located within said furnace chamber, and said
high-temperature area maintaining a high temperature range from 1400
degree C. to 1600 degree C.;retaining said molds filled with said
liquidized silicon in said high-temperature area for 2 to 8
hours;transporting said molds filled with said liquidized silicon from
said high-temperature area to a medium-temperature area for 10 to 30
hours, thereby gradually solidifying said liquidized silicon to form
crystallized silicone; wherein, said medium-temperature disposed in said
furnace chamber area having a medium temperature range from 1100 degree
C. to 1400 degree C.;forwarding said crystallized silicon in said molds
through a low-temperature area for 10 to 20 hours and decreasing said
medium temperature gradient within a temperature range between 600 degree
C. and 1000 degree C.; wherein, said low-temperature area disposed in
said furnace chamber having a low temperature range from 600 degree C. to
1100 degree C.; and thereaftercooling said crystallized silicon inside
said molds gradually from said low temperature to a room temperature
under an assistance of a shroud in a rotary conveyer track, thus
generating an integral solidification of polysilicon ingot.

2. The directional solidifying method for incessantly producing
polysilicon ingot as claimed in claim 1, where, some Argon gas is
conducted into said high-temperature area for controlling an atmosphere
of said liquidized silicon.

4. The directional solidification method for incessantly producing
polysilicon ingot as claimed in claim 3, wherein, said empty graphite
molds have their outer and inner surfaces coated with either Silicon
Nitride (Si3N4) or Boron Nitride (BN) as an antioxidant.

6. The method of directional solidification for incessantly producing
polysilicon ingot as claimed in claim 3, wherein, said empty graphite
molds have their inner surfaces coated with Boron Nitride (BN) and their
outer surfaces coated with Silicon Nitride (Si3N4).

7. An ingot casting apparatus for incessantly producing polysilicon ingots
comprising:a furnace body; wherein, said furnace body being sectional and
detachable;a furnace chamber disposed inside said body; wherein, said
chamber comprising in sequence a preheating area, a high-temperature
area, a medium-temperature area, and a low-temperature area axially
disposed therein; said high-temperature area having a furnace hopper
attached to a crown thereof for pouring liquidized silicon in;a plurality
of furnace cars disposed below said furnace chamber for loading a
plurality of graphite molds;a furnace track arranged under said furnace
cars, by which said cars can follow said track into said furnace
chamber;a front auxiliary car disposed in front of a furnace entrance for
assisting said furnace cars back to said entrance;a rear auxiliary car
disposed behind a furnace exit for driving said furnace cars back to said
rotary conveyer track;a rotary conveyer track disposed at both sides of
said furnace body for transporting said furnace cars from said exit
toward said entrance;a propulsion apparatus disposed in front of said
furnace entrance for propelling said furnace cars forward into said
furnace chamber; wherein, said apparatus can be utilized by hydrostatic
or mechanical propulsions; andan electricity and temperature adjusting
system disposed outside said furnace body.

8. The ingot casting apparatus for incessantly producing polysilicon
ingots as claimed in claim 7, wherein, said furnace hopper is a
conductive charging hopper for pouring said liquidized silicon into said
graphite molds.

9. The ingot casting apparatus for incessantly producing polysilicon
ingots as claimed in claim 7, wherein, said furnace hopper has a hopper
outer sleeve disposed thereon, and said hopper outer sleeve is secured to
said furnace body.

10. The ingot casting apparatus for incessantly producing polysilicon
ingots as claimed in claim 8, wherein, said furnace hopper has a hopper
outer sleeve disposed thereon, and said hopper outer sleeve is secured to
said furnace body.

11. The ingot casting apparatus for incessantly producing polysilicon
ingots as claimed in claim 6, wherein, said rotary conveyer track
adjacent to said furnace exit includes a shroud arranged thereon.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The invention patent relates to a metallurgical method for
incessantly manufacturing polysilicon ingot based on the polycrystalline
materials and its ingot casting apparatus.

[0003]2. Description of the Related Art

[0004]Currently, the issue on the solar-grade energy has been highly
concerned by relevant industries, and the polysilicon ingot is one of the
popular elements applying to the solar cells. In practical, it generally
contains two methods for producing polysilicon ingots; one is a heat
exchanging method, generally adopted by some famous companies in Japan,
Germany, and France, namely melting the raw silicon material by a
crucible and then passing it through the bottom of the crucible for
proceeding to cool and thereafter form an integral ingot; the other
method is to arrange two respective crucibles for melting and cooling the
material into the integral ingot. The heating exchanging method may
benefit to produce 250 KG of integral ingots, but it has the
disadvantages of higher energy consumption, longer periodic time, and
only single integral ingot produced by one casting furnace.

[0005]Of further method for producing ingots, The China Patent no.
CN1873062 discloses a method for producing high dense polycrystalline
cell and its apparatus, mainly applying the concatenation of the vacuum
electromagnetic induction melting, the plasma oxidation, and the eutectic
solidification for manufacturing the solar silicon ingot. Theoretically,
the electromagnetic induction reactor mainly describes that the
electromagnetic field exchanges outside the materials and the equation as
below is required to be satisfied: `Q=J2/i`. Further, according to the
chemical equilibrium, the equilibrium partial pressure of element is
lower than the pressure the atmosphere, thus the vacuum melting method
can eliminate the impurities inherent within the liquidized silicon. In
view of the theory of metal solidification, the elements having the
equilibrium distribution coefficient smaller than 1 are obviated from the
liquid.

[0006]Additionally, according to the China patent No. CN 85100529, it
discloses a process of solidifying the polycrystalline cell, comprising
the steps of hanging the graphite molds in time of melting the raw
silicon materials; fastening the molds to the rotating shaft and further
descending the molds while increasing the water flow speed for
water-cooling the melted silicon from the bottomless crucible, thereby
producing the integral silicon ingot formed in pillar shape with no holes
and cracks therein and the centimeter width. However, the above two cited
references can merely produce one silicon ingot per time while utilizing
one furnace, thus still requires improvements.

SUMMARY OF THE INVENTION

[0007]The purpose of the present invention is to provide a metallurgical
method, which is conducive to incessantly produce large amount of
polysilicon ingots, thus improving the conventional method of one ingot
produced by one casting apparatus.

[0008]Another purpose of the present invention is to provide an ingot
casting apparatus applied to cast larger quantities of the integral
polysilicon ingots in single producing line.

[0009]Furthermore, the ingot casting apparatus of the present invention
for incessantly producing polysilicon ingots mainly comprises a furnace
body, a furnace chamber disposed therein, furnace cars disposed below the
chamber for following a furnace track into the chamber, graphite molds
loaded by the cars, a front and a rear auxiliary cars, a rotary conveyer
track for controlling the movements of the cars, a propulsion apparatus
disposed in front of the furnace entrance, and an electricity and
temperature adjusting system disposed outside the body. While in use, the
molds are sequentially arranged in the chamber and preheated in the
preheating area, further the liquidized silicon is poured into the molds
and retains in a high temperature area, thence gently solidified in
medium-temperature area, thereafter decreasing the temperature in the
low-temperature area, and finally cooled down to the room temperature
under the protection of a shroud on the rotary conveyer track, thus
finishing the integral ingot. Moreover, the preheated molds loaded by the
furnace cars generate a high-low temperature layer therein, and which
results of the liquidized silicon therein forming a solid-liquid property
from the bottom to the top, which is thereafter solidified into a pillar
contour, thus simultaneously eliminating the impurities inside the
liquid.

[0010]The advantages of the present invention over the known prior art
will become more apparent to those of ordinary skilled in the art upon
reading the following descriptions in junction with the accompanying
drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a schematic view showing an ingot casting apparatus of the
present invention; and

[0012]FIG. 2 is a top view showing the ingot casting apparatus of the
present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013]Referring to FIGS. 1 and 2, an ingot casting apparatus of the
present invention comprises a furnace body, a furnace chamber 15 disposed
therein, furnace cars 2 disposed for loading a plurality of graphite
molds 1, a furnace track 18 arranged under the furnace cars 2, a front
auxiliary car 20, a rear auxiliary car 16, a rotary conveyer track
disposed around the chamber 15 for controlling the movements of the cars
2, a propulsion apparatus disposed in front of the furnace chamber 15,
and an electricity and temperature adjusting system disposed outside the
body; wherein, the furnace body is sectional and detachable, and both
sides thereof have respective windows for users to be aware of the
charging status of the liquidized silicon 4.

[0014]Still further, the furnace chamber 15 disposed inside the furnace
body has a security door at an entrance thereof for preventing the
malposition of the cars 2, which can be detected by a protection device,
and further comprises in sequence a preheating area 3, a high-temperature
area 5, a medium-temperature area 10, and a low-temperature area 11
axially disposed therein, thus generating a high-low temperature layer
within the chamber 15 in cross section. The above temperature areas are
respectively heated by an electric resistance filament, a SiC heater
element, and a MoSi2 heating element and are adjusted by a meter with a
PID controller, which are disposed in alignment for communicating with
computers and set up the appropriate temperature of each area; further,
the high-temperature area 5 has a gas inlet bore 7 disposed thereon for
conducting gas to control the atmosphere of liquidized silicon 4, e.g.
the Argon gas 8, and the above different temperature areas respectively
include outlet gas bore for obviating waste gas, adjusting the furnace
pressure and the balance of the gas flow. Additionally, the
high-temperature area 5 provides with a furnace hopper 6 attached to a
crown thereof and the furnace hopper 6 preferably belongs to a conductive
charging hopper fabricated of corundum materials and has an outer sleeve
thereon secured to the furnace body and an inner sleeve disposed therein.
Both the inner sleeve and the hopper 6 can be replaced if necessary.

[0015]Additionally, the furnace cars 2 is disposed below the chamber 15
for loading a plurality of graphite molds 1; each car 2 consists of metal
flames with four wheels and heat proofing layers and has proofing
sections at the bottom and by the sides thereof for absorbing and
discharging the leaking liquidized silicon 4 and also has relieving
pieces at the rear thereof for reducing the vibration while the car is
intermittently forwarding along the track. Furthermore, the furnace track
18 is arranged at the bottom of the furnace body, under the furnace cars
2; the front auxiliary car 20 is disposed in front of the furnace
entrance to help the furnace cars 2 back to the entrance along the rotary
conveyer track, and the rear auxiliary car 16 is disposed behind a
furnace exit to drive the furnace cars 2 back to the rotary conveyer
track 18 while approaching to the furnace exit, further the rotary
conveyer track is arranged at both sides of the furnace body for
transporting the cars 2 from the exit to the entrance and preferably
arranges a shroud adjacent to the exit for proceeding to the cooling
procedure. The propulsion apparatus is located in front of said furnace
entrance for propelling the furnace cars 2 into the furnace chamber 15
and is utilized by hydrostatic or mechanical propulsions; further the
apparatus has a warning device for reminding of the abnormal state in
operation.

[0016]Still, the graphite molds 1 loaded by the furnace cars 2 are applied
to be resistant to oxidation, namely the molds 1 can have their outer and
inner surfaces coated with either Silicon Nitride (Si3N4) or Boron
Nitride (BN) as an antioxidant, have the inner surfaces coated with
Silicon Nitride (Si3N4) and the outer surfaces coated with Boron Nitride
(BN), or have the inner surfaces coated with Boron Nitride (BN) and the
outer surfaces coated with Silicon Nitride (Si3N4). Here it is adopted to
have the inner surfaces coated with Silicon Nitride (Si3N4) and the outer
surfaces coated with Boron Nitride (BN).

[0017]Referring to FIGS. 1 and 2, while in operation, the empty graphite
molds 1 are sequentially disposed on the furnace cars 2, which are then
forwarded by the front auxiliary car 20 to the front of the furnace door
13, and the propulsion apparatus 14 pushes the car 20 into the chamber
15, whereby preheating the molds 1 on the furnace cars 2 in the
preheating area 3 at the temperature from 1200 degree C. to 1600 degree
C. for 2 to 6 hours; then pouring the liquidized silicon 4 into the
preheated molds 1 by the furnace hopper 6 and retaining the molds 1 in
the high-temperature area 5 in a high temperature range of 1400 degree C.
to 1600 degree C. for 2 to 8 hours; simultaneously the Argon atmosphere 8
is conducted therein through the gas inlet bore 7. Thereafter, the molds
1 are forwarded from the high-temperature area 5 to the
medium-temperature area 10 in a temperature range from 1100 degree C. to
1300 degree C., for 10 to 30 hours, thus obtaining crystallized silicon
therein, and thereafter the molds 1 are transported to the
low-temperature area 11 in the temperature gradient range between 600
degree C. and 800 degree C. Then the rear auxiliary car 16 helps pushing
the cars 2 back to the rotary conveyer track and the crystallized silicon
is cooled until reaching the room temperature under the assistance of the
shroud of the rotary conveyer track, thus generating an integral
polysilicon ingot, and which requires 20 to 50 hours for an entire
producing process. Furthermore, the furnace cars 2 still shuttles on the
track when in turn to the furnace door 13. Therefore, the preheated molds
loaded by the furnace cars generate a high-low temperature layer therein,
and which results of the liquidized silicon 4 therein forming a
solid-liquid property from the bottom to the top, which is thereafter
solidified into a pillar contour, thus simultaneously eliminating the
impurities inside the liquid.

[0018]According to the aforementioned, the present invention has following
advantages:

1. Producing without interruption

[0019]By means of the configuration of the rotary conveyer track, the
present invention incessantly produces large amount of integral ingot per
time, so as to overcome the problem of lower quantities, longer period
manufacturing time, and merely one ingot produced by single casting
furnace occurred in the conventional method.

2. Retaining lower energy consumption and manufacturing cost

[0020]The arrangements of different temperature areas in the furnace
chamber facilitate to maintain the temperature in a certain range and
thereafter gradually cool the graphite molds by passing therethrough,
which results of consuming less energy and lowering the cost of
production.

3. Higher yield rate

[0021]In view of the sequential arrangement and intermittent movement of
the furnace cars and accompanying with the temperature adjusting system,
the present invention maintain to produce the integral polysilicon ingots
by the same producing line, thereby increasing the producing stability
and obtaining higher yield rate.

4. Uncomplicated equipments and technology

[0022]According to the aforementioned method, the present invention
utilizes single equipment and facile manipulations for increasing the
quantities of the ingots, for instance of producing more than 200 tons of
ingots by single furnace per year, whereby the method can efficiently
decrease the costs.

[0023]To sum up, the present invention mainly has a rotary device disposed
around the furnace body for intermittently inching the graphite molds
from the high-temperature area to the low-temperature area thereby, thus
adjusting the solidification of the crystallized by means of the
forwarding speed of the cars and the differentiated temperature among the
areas of the chamber. Further, the preheated molds loaded by the furnace
cars generate a high-low temperature layer therein to result of the
liquidized silicon therein forming a solid-liquid property, which is
thereafter solidified into a pillar contour and thence cooled until
reaching the room temperature, thus the integral polysilicon ingot is
finished and simultaneously the rotary conveyer track assists to
continuously produces ingots while manipulating.

[0024]While we have shown and described the embodiment in accordance with
the present invention, it should be clear to those skilled in the art
that further embodiments may be made without departing from the scope of
the present invention.